Prior to performing a surgical operation on a part of the body, such as for example the arms or legs, it may be desirable to perform a nerve block in order to anesthetize a nerve bundle in a part of the body proximate to where surgery will occur. Often, a catheter-based infusion system is utilized to both block the nerve bundle for surgery and to provide a continuous, low flow rate of the anesthetic over a period of time (e.g., 2-3 days following surgery) for post-operative pain management.
One approach is to introduce an epidural-type needle or needle and peel-away-type sheath into the general area of the desired nerve bundle. Once proper location of the needle is achieved, a test dose of the anesthetic may be provided through the epidural needle and a catheter may be introduced through the needle to administer the anesthetic and maintain the nerve block.
Several methods of targeting needle location exist today—insulated needles having an integral conductive wire such that a small amount of current may be pulsed through the needle or catheter by a nerve stimulator (i.e., a current generator). An electrical current of 0.1 to about 2 mA will induce motor movement in the patient when the tip of the needle (frequently called a “stimulating needle”) is near the nerve. When the stimulating needle is probed into the general area of the desired nerve bundle, the pulsing current stimulates the nerve and causes a motor response to assist in properly locating the needle. As the current is reduced, the motor effect is also reduced so a needle that causes movement at a low current is likely to be very close to the desired area for drug delivery.
One problem with this approach is that the catheter insertion through the needle may move the tip of the needle away from the target zone. Alternatively and/or additionally, the tip of the catheter may curl away from the target zone during insertion.
Several manufacturers have designed stimulating catheters that correct this problem by passing the current first through the needle and then separately through the catheter. The problem with this is that the catheter cannot be steered to the target zone without risking pulling back through the needle and potentially damaging the catheter. In addition, the additional time needle to place and maneuver the catheter is significant and after the catheter is secured, it can dislodge by patient movement and then become ineffective.
Ultrasound guided techniques have added imaging to the procedure, but they are mainly used to see the adjacent vessels and are not always good at seeing the needle and/or catheter. The problem with ultrasound guided techniques is that the needle and catheter cannot be easily seen through tissue. That is, the ability to see the tip and/or other portions of the needle and/or catheter under ultrasound imaging techniques is limited. Another problem is that conventional catheters do not allow one to place the catheter quickly allowing for some small migration or tip mis-positioning while still delivering drug to the target area.
A variety of approaches have been used to enhance ultrasonic imaging of medical devices by increasing the acoustic reflection coefficient of the devices. In U.S. Pat. No. 4,401,124 issued to Guess et al., the reflection coefficient of a biopsy needle is enhanced by the use of a diffraction grating disposed on the surface of the needle. A variety of mechanisms for enhancing the ultrasound image of a portion of a medical instrument are also disclosed in U.S. Pat. No. 5,289,831 issued to Bosley, U.S. Pat. No. 5,201,314 issued to Bosley et al. and U.S. Pat. No. 5,081,997, also issued to Bosley et al. These patents disclose catheters and other devices provided with echogenic surfaces including spherical indentations or projections in the range of 0.5 to 100 microns or fabricated of material incorporating glass spheres or high density metal particles in the range of 0.5 to 100 microns. The use of micro-bubbles introduced into polymers to provide echogenic catheter components is described in U.S. Pat. No. 5,327,891, issued to Rammler.
However, these features add complexity to manufacturing and may negatively impact the performance of a catheter having a plurality of exit holes along a portion of the catheter. For example, glass beads adhered to the exterior of a catheter may become dislodged. Glass beads incorporated into the polymer matrix may create difficulties during creation of exit holes. Microbubbles formed in the polymer matrix of the catheter wall can be difficult to form reliably during the extrusion process. Spherical indentations or spherical protuberances can be challenging and/or expensive to form on a single use item. For example, an EchoTip® Ultrasound Needle has a plurality of spherical indentations that can increase acoustic reflection. However, these spherical indentations can be difficult or expensive to produce in a metal needle and may be ineffective when implemented in items that are generally not very acoustically reflective such as, for example, a polymer catheter.